This invention is generally in the field of waste treatment, and particularly in the area of recycling of fish wastes.
Disposal of fish wastes using conventional technology presents a number of problems Of primary importance is the odor associated with the long-term storage of the fish wastes Other problems include the cost of disposal and EPA regulations which prohibit dumping of fish wastes into the sewer or harbor water.
Historically, after extraction of useful oils, fish wastes have been rendered by a cooking process into a fish meal. Due to the odorous nature of this rendering process and to poor market conditions, many waste processing companies are having great difficulties in operating profitably and have been forced to close down.
Chemicals have also been used to aid in the disposal of fish wastes. For example, a strong base such as potassium hydroxide may be used to hydrolyze the fish wastes. U.S. Pat. No. 3,598,606 teaches a process for making a fish meal using sodium hexametaphosphate to insolubilize protein fractions. U.S. Pat. No. 4,043,788 to Fryer discloses a process for making a fertilizer by combining neutralized, hydrolyzed fish or fish waste with a solubilized seaweed and chelated plant nutrients. The fish is hydrolyzed by boiling in potassium hydroxide. U.S. Pat. No. 4,383,845 to Rutherford also discloses a foliar growth-promoting mixture including a liquid seaweed base, a fish emulsion consisting of fish solids which have been degraded under pressure with heat on the addition of an alkaline composition, liquid humus, and a mixture of carbohydrates, enzymes, and vitamins. The disadvantages of these processes are that they use strong chemical bases and heat or pressure to degrade the fish wastes, there is no method for eliminating the odor problem, and there is no process for handling high concentrations of fish oil such as that found in wastes from fish species such as menhaden or herring.
As shown by Torpey U.S. Pat. No. 3,259,566 and Ghosh et al., U.S. Pat. No. 4,022,665, anaerobic digestion has been used to convert organic wastes such as human sewage into a biogas consisting mainly of methane and carbon dioxide and other simple organic compounds. However, high oil contents from some fish species could cause mixing problems if conventional digestion apparatus were used.
It is therefore an object of the invention to provide a method and apparatus for disposal of fish and fish wastes in an economical, environmentally acceptable way, which is relatively odor-free.
It is a further object of the invention to provide a method and apparatus for producing commercially useful by-products of the disposal of fish wastes.
It is a still further object of the invention to provide a method and apparatus for economically manufacturing fertilizer containing protein, trace elements, and micronutrients
It is another object of this invention to provide a method for disposal of fish wastes from fish species containing large amounts of fish oil without extensive chemical treatment.
It is a still further object of the invention to produce a stable digested fish wastes composition which does not contain viable pathogenic organisms or toxins.